1D Multi-element CMUT arrays for ultrasound thermal therapy

Interstitial therapeutic ultrasound devices are a promising technology for performing thermal ablation in a wide variety of organs. In this study, the use of Capacitive Micromachined Ultrasound Transducers (CMUTs) for interstitial heating applications was investigated. CMUTs exhibit potential advantages for use in therapeutic ultrasound applications in comparison to standard piezo ultrasound transducer technologies as they have good characteristics in terms of miniaturization (cell size: few dozens of microns), bandwidth (several MHz) and high electro-acoustic efficiency. Two designs of CMUT arrays were studied: (1) a 1D 128-element planar-CMUT array originally dedicated to abdominal ultrasound imaging purposes (5 MHz, element size: 0.3 x 8.0 mm(2)); (2) a 12-element linear-array, 32.4-mm long and 0.8-mm wide, developed specifically for minimally-invasive interstitial therapeutic applications (6 MHz, element size: 2.7 x 0.8 mm(2)). Simulations were performed to evaluate the ability to generate thermal lesions in soft tissues with: (1) 1 single linear array, (2) a combination of multiple linear arrays positioned on a cylindrical catheter. Experimental investigations performed with the CMUT imaging array showed the ability to generate surface acoustic intensities (I-ac) up to 20 W . cm(-2) and to generate intense centimetric thermal lesions in in-vitro turkey breast tissues. At 6 MHz, a single element was able to generate in water a maximum peak pressure of >0.5 MPa. In simulations, the ability to use various power levels and frequencies on independent elements, as well as combinations of multiple linear-arrays offered sufficient flexibility to achieve a wide variety of thermal ablation patterns in 3D. Simulated ablation volumes could be controlled to cover accurately non-symmetrical volumes of brain metastases. In conclusion, CMUT arrays show interesting characteristics, which may open new perspectives of spatial control for conformal interstitial thermal therapy with miniaturized multi-element therapeutic ultrasound catheters.